Coated optical fiber and curable compositions suitable for coating optical fiber

ABSTRACT

The present invention provides materials suitable for use as secondary coatings of optical fibers or the re-coating of spliced optical fiber junctions. With regard to the latter use, the coating materials a preferably characterized by a Young&#39;s modulus that is at least about 1200 MPa, and an interfacial strength as measured by the rod and tube method of greater than 25 MPa.

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/454,984, now U.S. Pat. No. 6,862,392, filed Jun. 4, 2003which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to optical fiber, and moreparticularly to coatings for optical fiber and to curable compositionsfor use in coating optical fiber.

2. Technical Background

Optical fiber has acquired an increasingly important role in the fieldof telecommunications, frequently replacing existing copper wires. Thistrend has had a significant impact in all areas of telecommunications,greatly increasing the amount of data that is transmitted. Furtherincrease in the use of optical fiber is foreseen, especially in metroand fiber-to-the-home applications, as local fiber networks are pushedto deliver an ever-increasing volume of audio, video, and data signalsto residential and commercial customers. In addition, use of fiber inhome and commercial premise networks for internal data, audio, and videocommunications has begun, and is expected to increase.

Optical fiber is typically made of glass, and usually has a polymericprimary coating and a polymeric secondary coating. The primary coating(also known as an inner primary coating), is typically applied directlyto the glass fiber, and when cured forms a soft, elastic, compliantmaterial encapsulating the glass fiber. The primary serves as a bufferto cushion and protect the glass fiber during bending, cabling orspooling. The secondary coating (also known as an outer primary coating)is applied over the primary coating, and functions as a tough,protective outer layer that prevents damage to the glass fiber duringprocessing, handling and use.

The secondary coatings conventionally used in optical fibers aretypically crosslinked polymers formed by curing a mixture of an oligomer(e.g. a urethane (meth)acrylate) and at least one monomer (e.g. a(meth)acrylate monomer). Generally, a high Young's modulus is desired inorder to provide increased hardness of the protective material. However,an increase in Young's modulus generally serves to increase thebrittleness of the material, making it more likely to crack during use.As such, current optical fiber secondary coatings tend to have lowerthan desirable Young's moduli in order to ensure the necessaryrobustness.

SUMMARY OF THE INVENTION

One embodiment of the present invention relates to a coated opticalfiber comprising: first and second optical fiber segments, eachincluding an optical fiber having at least one coating thereon, which atleast one coating has been removed from an end section thereof, the endsections of the first and second optical fiber segments abutting oneanother end-to-end; and a cured splice-junction coating thatencapsulates the end sections and contacts the at least one coating ofthe first and second optical fiber segments, wherein the splice-junctioncoating is characterized by

a Young's modulus that is at least about 1200 MPa and an interfacialstrength as measured by the rod and tube method of greater than about 25MPa, more preferably greater than 35 MPa.

Another embodiment of the present invention relates to a method ofre-coating an optical fiber at a splice junction, where method includesthe steps of: providing first and second optical fiber segments, eachcomprising an optical fiber having at least one coating thereon, whichat least one coating has been removed from an end section thereof, theend sections of the first and second optical fiber segments abutting oneanother end-to-end; applying a coating composition to the end sectionsof the first and second optical fibers, whereby the coating compositionencapsulates the end sections and contacts the at least one coating ofthe first and second optical fiber segments; and curing the coatingcomposition to form a cured splice-junction coating that ischaracterized by

-   -   (i) a Young's modulus that is at least about 1200 MPa, and    -   (ii) an interfacial strength as measured by the rod and tube        method of greater than about 25 MPa, more preferably greater        than 35 MPa.

Another embodiment of the present invention relates to a coated opticalfiber comprising:

first and second optical fiber segments, each comprising an opticalfiber having at least one coating thereon, which at least one coatinghas been removed from an end section thereof, the end sections of thefirst and second optical fiber segments abutting one another end-to-end;and

a cured splice-junction coating that encapsulates the end sections andcontacts the at least one coating of the first and second optical fibersegments;

wherein the splice-junction coating is characterized by

-   -   (i) a Young's modulus that is at least about 1200 MPa, and    -   (ii) and a puncture resistance yin grams greater than about        0.0019x+11.255, where x=the cross sectional area in microns² of        the coating.

Another embodiment of the present invention relates to a method ofre-coating an optical fiber at a splice junction, said methodcomprising:

providing first and second optical fiber segments, each comprising anoptical fiber having at least one coating thereon, which at least onecoating has been removed from an end section thereof, the end sectionsof the first and second optical fiber segments abutting one anotherend-to-end; and

applying a coating composition to the end sections of the first andsecond optical fibers, whereby the coating composition encapsulates theend sections and contacts the at least one coating of the first andsecond optical fiber segments; and

curing the coating composition to form a cured splice-junction coatingthat is characterized by

-   -   (i) a Young's modulus that is at least about 1200 MPa, and    -   (ii) a puncture resistance y in grams greater than about        0.0019x+11.255, where x=the cross sectional area in microns² of        the coating.

The optical fibers, methods, and curable compositions of the presentinvention result in a number of advantages over prior art devices andmethods. The optical fibers of the present invention have secondarycoatings with high Young's moduli, and are therefore well-protected fromenvironmental abuse and exhibit reduced sensitivity to microbending.Simultaneously, the optical fibers of the present invention exhibitimproved handleability due to the high fracture toughness and highductility of the secondary coating. Optical fibers according to thepresent invention may also have secondary coatings having a lowsensitivity to the formation of defects.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from the description or recognizedby practicing the invention as described in the written description andclaims hereof, as well as in the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings are not necessarily to scale,and sizes of various elements may be distorted for clarity. The drawingsillustrate one or more embodiment(s) of the invention, and together withthe description serve to explain the principles and operation of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a coated optical fiber according oneembodiment of the present invention;

FIG. 2 is a schematic view of a film sample used in the measurement offracture toughness;

FIG. 3 is a set of atomic force microscopy (AFM) phase maps;

FIG. 4 is a schematic view of an optical fiber ribbon according to anembodiment of the present invention;

FIG. 5 is a schematic view of an optical fiber including a marking inkaccording to an embodiment of the present invention; and

FIG. 6 is a side elevational view of a recoated optical fiber, with aportion of the cured recoat broken away to expose the underlying splicejunction.

FIG. 7 illustrates fiber positioning for the puncture resistance testdescribed below.

FIG. 8 illustrates puncture load vs. cross sectional area for a varietyof coatings.

FIG. 9 illustrates a specimen used in a adhesion test, as describedfurther below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present invention relates to a coated opticalfiber. An example of a coated optical fiber is shown in schematiccross-sectional view in FIG. 1. Coated optical fiber 20 includes a glassoptical fiber 22 surrounded by primary coating 24 and secondary coating26. The secondary coating is formed from a cured polymeric materialhaving a Young's modulus of at least about 1200 MPa and a fracturetoughness of at least about 0.7 MPa·m^(1/2).

The glass fiber 22 is an uncoated optical fiber including a core and acladding, as is familiar to the skilled artisan. The uncoated opticalfiber may be a single mode fiber, or a multimode fiber. The opticalfiber may be adapted for use as a data transmission fiber (e.g. SMF-28®,LEAF®, and METROCOR®, each of which is available from CorningIncorporated of Corning, N.Y.). Alternatively, the optical fiber mayperform an amplification, dispersion compensation, or polarizationmaintenance function. The skilled artisan will appreciate that thecoatings described herein are suitable for use with virtually anyoptical fiber for which protection from the environment is desired.

In coated optical fiber 20, glass fiber 22 is surrounded by a primarycoating 24. Primary coating 24 is formed from a soft crosslinked polymermaterial having a low Young's modulus (e.g. less than about 5 MPa at 25°C.) and a low glass transition temperature (e.g. less than about −10°C.). The primary coating 24 desirably has a higher refractive index thanthe cladding of the optical fiber in order to allow it to strip errantoptical signals away from the optical fiber core. The primary coatingshould maintain adequate adhesion to the glass fiber during thermal andhydrolytic aging, yet be strippable therefrom for splicing purposes. Theprimary coating typically has a thickness in the range of 25–40 μm (e.g.about 32.5 μm). Primary coatings are typically applied to the glassfiber as a liquid and cured, as will be described in more detailhereinbelow. Conventional curable compositions used to form primarycoatings are formulated using an oligomer (e.g. a polyether urethaneacrylate), one or more monomer diluents (e.g. ether-containingacrylates), a photoinitiator, and other desirable additives (e.g.antioxidant). Primary coatings for optical fibers have beenwell-described in the past, and are familiar to the skilled artisan.Desirable primary coatings are disclosed in U.S. Pat. Nos. 6,326,416;6,531,522; and 6,539,152; U.S. patent application Publication No.2003/0049446; and U.S. patent application Ser. Nos. 09/712,56;09/916,536; and 10/087,481, each of which is incorporated herein byreference in its entirety. Another desirable primary coating is thecured reaction product of a primary coating composition including 52 wt% BR3741 (Bomar Specialties); 25 wt % PHOTOMER 4003 (Cognis); 20 wt %TONE M-100 (Dow Chemical); 1.5 wt % IRGACURE 819 (Ciba); 1.5 wt %IRGACURE 184 (Ciba); 1 pph (3-acryloxypropyl)trimethoxysilane (Gelest);and 0.032 pph pentaerythritol tetrakis(3-mercaptoproprionate) (Aldrich).

In coated optical fiber 20, primary coating 24 is surrounded bysecondary coating 26. While in FIG. 1, the secondary coating is shown asbeing applied directly to the primary coating, the skilled artisan willrecognize that there may be one or more intermediate coating layersdeposited between the primary coating and the secondary coating.Secondary coating 26 is formed from a cured polymeric material, andtypically has a thickness in the range of 20–35 μm (e.g. about 27.5 μm).The secondary coating desirably has sufficient stiffness to protect theoptical fiber; is flexible enough to be handled, bent, or spooled; haslow tackiness to enable handling and prevent adjacent convolutions on aspool from sticking to one another; is resistant to water and chemicalssuch as optical fiber cable filling compound; and has adequate adhesionto the coating to which it is applied (e.g. the primary coating).

The cured polymeric material of secondary coating 26 of optical fiber 20has a Young's modulus of at least about 1200 MPa. In desirableembodiments of the invention, the cured polymeric material of secondarycoating 26 has a Young's modulus of at least about 1500 MPa. Inespecially desirable embodiments of the invention, the cured polymericmaterial of secondary coating 26 has a Young's modulus of at least about1900 MPa. In desirable embodiments of the invention, the cured polymericmaterial of secondary coating 26 has an elongation to break of at leastabout 30%. In especially desirable embodiments of the invention, thecured polymeric material of secondary coating 26 has an elongation tobreak of at least about 40%. In desirable embodiments of the invention,the cured polymeric material of secondary coating 26 has an averagetensile strength of at least about 48 MPa. In especially desirableembodiments of the invention, the cured polymeric material of secondarycoating 26 has an average tensile strength of at least about 60 MPa. Asused herein, the Young's modulus, elongation to break, and tensilestrength of a cured polymeric material are measured using a tensiletesting instrument (e.g. a Sintech MTS Tensile Tester, or an InstronUniversal Material Test System) on a sample of a material shaped as acylindrical rod about 0.0225″ (571.5 μm) in diameter, with a gaugelength of 5.1 cm, and a test speed of 2.5 cm/min.

The resistance of a material to unstable, catastrophic crack growth isdescribed by the material property known as fracture toughness, K_(IC).The fracture toughness of a material relates to the energy required topropagate a crack in the material. The cured polymeric material ofsecondary coating 26 of optical fiber 20 has a fracture toughness of atleast about 0.7 MPa·m^(1/2). In desirable embodiments of the invention,the cured polymeric material of the secondary coating has a fracturetoughness of at least about 0.9 MPa·m^(1/2). In especially desirableembodiments of the invention, the cured polymeric material of thesecondary coating has a fracture toughness of at least about 1.1MPa·m^(1/2). In certain embodiments of the invention, the curedpolymeric material of the secondary coating has a fracture toughness ofat least about 1.3 MPa·m^(1/2). As used herein, fracture toughnessK_(1C) is measured on film samples, and is defined as Yσ√{square rootover (z)}, where Y is a geometry factor, σ is the tensile strength (atbreak) of the film sample, and z is half of the notch length. Fracturetoughness is measured on films having a center cut notch geometry. FIG.2 is a schematic depiction of the sample geometry used in measuringfracture toughness. Film sample 80 has a width of about 52 mm, and isabout 0.010″ (254 μm) in thickness. A notch 82 is cut in the center ofthe film using a sharp blade using methods familiar to the skilledartisan. Notches having lengths of 18 mm, 24 mm, and 30 mm are cut indifferent samples. The tensile strength (at failure) of the sample, σ,is measured using a tensile testing instrument (e.g. a Sinitech MTSTensile Tester, or an Instron Universal Material Test System), asdescribed above. The sample is gripped in the jaws 84 of the tensiletesting instrument such that the gauge length is 75 mm. The displacementrate is 2.0 mm/min. The tensile strength may be calculated by dividingthe applied load at failure by the cross-sectional area of the intactsample. For the samples described above, the tensile strength may becalculated using the equation

$\sigma = {\frac{Load}{254\mspace{14mu}{{µm}\left( {{52\mspace{20mu}{mm}} - {2z}} \right)}}.}$

The sensitivity of the cured polymeric material of the secondary coatingto handling and the formation of defects is reflected by its ductility.The ductility of a material is defined by the equation

${Ducility} = {\left( \frac{K_{IC}}{{yield}\mspace{20mu}{stress}} \right)^{2}.}$Larger ductilities indicate reduced sensitivity of the secondary coatingto handling and defect formation. Yield stress can be measured on therod samples at the same time as the Young's modulus, elongation tobreak, and tensile strength, as described above. As is familiar to theskilled artisan, for samples that exhibit strain softening, the yieldstress is determined by the first local maximum in the stress vs. straincurve. More generally, the yield stress can be determined using themethod given in ASTM D638-02, which is incorporated herein by referencein its entirety. In desirable embodiments of the present invention, thecured polymeric material of the secondary coating has a ductility of atleast about 314 μm. In especially desirable embodiments of the presentinvention, the cured polymeric material of the secondary coating has aductility of at least about 376 μm. In certain embodiments of thepresent invention, the cured polymeric material of the secondary coatinghas a ductility of at least about 471 μm.

The coated optical fibers according to one embodiment of the presentinvention exhibit single fiber strip forces comparable to those ofoptical fibers having secondary coatings with lower fracture toughness.Desirable coated optical fibers of the present invention have singlefiber strip forces of less than about 1 pound force at a temperature of23° C. Especially desirable coated optical fibers of the presentinvention have single fiber strip forces of less than about 0.8 poundsforce at a temperature of 23° C. Strip forces are determined using amethod according to FOTP-178, which is incorporated herein by referencein its entirety. Coated fibers are placed into a load cell, and thenstripped at a rate of 0.847 cm/second under environmental conditions of23° C. and 50% relative humidity.

The cured polymeric materials used in the secondary coatings of theoptical fibers of the present invention may be the cured product of acurable composition including an oligomer and at least one monomer. Asis conventional, the curable compositions used in forming the secondarycoatings may also include photoinitiators, antioxidants, and otheradditives familiar to the skilled artisan. In desirable embodiments ofthe invention, the oligomer and monomers of the curable composition areethylenically unsaturated. In especially desirable embodiments of theinvention, the oligomer and monomers of the curable composition are(meth)acrylate-based. The oligomer may be, for example, a urethane(meth)acrylate oligomer. However, as the skilled artisan will recognize,oligomers and monomers adapted for other curing chemistries, such asepoxy, vinyl ether, and thiol-ene, may be used in accordance with thepresent invention.

Desirably, the oligomer of the curable composition is selected toprovide both high modulus and high fracture toughness to the curedpolymeric material. The inventors have determined that oligomers thathave rigid polyol-derived subunits, multiple functionality, and/orcrystallizable moieties are especially desirable for use in the curablecompositions of the present invention. Oligomers are described herein bytheir average structure. For example, an oligomer prepared from 1.0equivalent of HO—R—OH; 2.0 equivalents of OCN—R_(I)—NCO; and 2.0equivalents of CAP—OH has the average structureCAP—OOC—NH—R_(I)—NH—[COO—R—OOC—NH—R_(I)—NH]_(1.0)—COO—CAP. While theoligomer is, in reality, a mixture of components (e.g., some with twodiol blocks, some with one diol block, and some with no diol blocks),the average structure of the oligomer is a weighted average of thecomponents. For cases in which reactants are combined to form anoligomer without subsequent purification, the average structure mayconveniently be defined by the stoichiometry of the reactants used tomake it.

The oligomers described herein may be synthesized using methods familiarto the skilled artisan, such as those described in U.S. Pat. No.4,6087,409 to Coady et al., and U.S. Pat. No. 4,609,718 to Bishop etal., each of which is incorporated herein by reference in its entirety.Typically, a polyisocyanate is reacted with a polyol to yield anisocyanate-terminated urethane oligomer, which is then capped with ahydroxy-functional capping agent having a reactive terminus (e.g.(meth)acrylate, epoxy, vinyl ether). Alternatively, the reaction betweenthe polyisocyanate and the polyol may yield a hydroxy-terminatedoligomer, which may be capped with an appropriate capping agent, such asan acid chloride or isocyanate, having a reactive functionality. Theskilled artisan may use diamines or polyamines in place of some or allof the diol or polyol to provide an oligomer having urea linkingmoieties.

As used in the examples described herein, polyisocyanates have thestructure R_(I)(NCO)_(j), where R_(I) is the polyisocyanate core moiety.The polyisocyanate is incorporated into the oligomer structure with thecore moiety R_(I) being linked into the oligomer by urethane (—NH—COO—)or urea (—NH—CO—NH—) bonds. A non-exhaustive list of polyisocyanatesthat may be desirable for use in the curable compositions of the presentinvention is given in Table 1, below.

TABLE 1 Chemical Name R₁ Structure4,4′-methylenebis(cyclohexyl-isocyanate) H12MDI

toluene diisocyanate TDI

isophorone diisocyanate IPDI

α,α,α′,α′-tetramethyl-1,3-xylylene diisocyanate TMXDI

tris(6-isocyanatohexyl)-isocyanurate HDIT

In the examples described herein, the capping agent has the structureCAP—OH, where the capping moiety CAP includes a reactive terminus (e.g.(meth)acrylate, epoxy, vinyl ether). In these examples, the cappingagent is linked into the oligomer structure by a urethane bond. Anon-exhaustive list of capping agents that may be desirable for use inacrylate-based curable compositions of the present invention is given inTable 2, below.

TABLE 2 Chemical Name R₁ Structure caprolactone acrylate CLA

(2-hydroxyethyl) acrylate HEA

pentaerythritol triacrylate PETA

(3-hydroxypropyl) acrylate HPA

(4-hydroxybutyl) acrylate HBA

monoacrylatedpoly(propylene glycol),M_(n)~475 Daltons PPGA

According to one embodiment of the invention, the oligomer has adiisocyanate-derived core linked to two capping moieties throughurethane bonds. One example of a suitable class of oligomers for use inthe curable compositions of the present invention has the structureCAP—OOC—NH—R_(I)—NH—COO—CAP,where CAP is a capping moiety having a reactive terminus, and R_(I) issubstantially free of urethane bonds. Desirably, at least 50 wt % of thetotal oligomer content of the formulation has the above structure.Desirably, the oligomer according to this embodiment of the inventionhas a number average molecular weight (M_(n)) of less than about 1600Daltons. In especially desirable embodiments of the invention, thisligomer has a M_(n) of less than about 1200 Daltons. Examples of sucholigomers includeCLA-OOC—NH—H12MDI—NH—COO—CLA;CLA-OOC—NH—IPDI—NH—COO—CLA; andCLA-OOC—NH-TMXDI—NH—COO—CLA.As the skilled artisan will appreciate, HEA-capped versions of theseoligomers may also be used.

According to another embodiment of the invention, the oligomer has anumber average molecular weight (M_(n)) of less than about 1600 Daltons.Examples of low molecular weight oligomers include[HEA-OOC—NH-TDI—NH—COO—PO2NPG-OOC—NH]₂TDICLA-OOC—NH—H12MDI—NH—COO—CLA;CLA-OOC—NH—IPDI—NH—COO—CLA; andCLA-OOC—NH-TMXDI—NH—COO—CLA,where PO2NPG is a propoxylated (1PO/OH) neopentyl glycol-derived moietyhaving the average structure (CH₃)₂C[CH₂OCH₂CH(CH₃)—]₂.

According to another embodiment of the invention, the oligomer has anaverage functionality (i.e. average number of reactive termini) greaterthan 2.2. Desirably, the oligomer has an average functionality of atleast about 3. One example of a suitable class of oligomers for use inthe curable compositions of the present invention has the averagestructureR_(M)[OOC—NH—R_(A)—NH—COO—CAP]_(n),where R_(M) is a multifunctional core moiety, n is greater than 2.2, andCAP is a capping moiety having a reactive terminus. In certainembodiments of the invention, R_(A) is an isocyanate-derived core moietyR_(I) that is substantially free of urethane bonds. In other embodimentsof the invention, R_(A) has the structure—R_(I)—(NH—COO—R_(C)—OOC—NH—R_(I))_(t)—, where R_(C) is a polyol-derivedcore moiety and t has an average value in the range of 0 to about 4.Certain desirable oligomers suitable for use in this embodiment of theinvention have number average molecular weights of less than about 3000Daltons. Examples of suitable members of this class of oligomers includePHOTOMER 6008;GlyPO₍₇₂₅₎[OOC—NH—H12MDI—NH—COO—HEA]₃;GlyPO₍₇₂₅₎[OOC—NH—H12MDI—NH—COO—CLA]₃;GlyPO₍₇₂₅₎[OOC—NH-TMXDI—NH—COO—CLA]₃;GlyPO₍₇₂₅₎[OOC—NH-TDI—NH—COO—CLA]₃;GlyPO₍₇₂₅₎[OOC—NH-TDI—NH—COO—PETA]₃PertPO₍₄₂₆₎[OOC—NH—H12MDI—NH—COO—CLA]₄;UMB2005[OOC—NH—H12MDI—NH—COO—HEA]_(2.4);TMPPO[OOC—NH—IPDI—NH—COO—PPG₍₄₂₅₎—OOC—NH—IPDI—NH—COO—HEA]₃; andTMPPO[OOC—NH—IPDI—NH—COO-T₍₆₅₀₎—OOC—NH—IPDI—NH—COO—HEA]₃,where UMB2005 is the residue of a hydroxy-functional (2.4 OH/molecule onaverage) poly(butyl acrylate) having an M_(n)˜2600 Daltons availablefrom Esprix Technologies; PertPO₍₄₂₆₎ is a propoxylated pentaerythritylmoiety having the average structure C[CH₂(OCHCH₃CH₂)_(x)—]₄; GlyPO₍₇₂₅₎is a propoxylated glyceryl moiety having an M_(n)˜725 Daltons and theaverage structure

and TMPPO is a propoxylated (1 propoxy/OH) trimethanolpropane moietyhaving the average structure

PHOTOMER6008 is an aliphatic urethane triacrylate oligomer availablefrom Cognis. The skilled artisan will recognize that other combinationsof R_(M), R_(A), and CAP can be used in the oligomers of this class.

Multiple functionality can also be achieved by the use of asubstantially linear oligomer backbone with a multifunctional cappingagent such as PETA. For example one suitable oligomer including amultifunctional capping moiety is PETA-OOC—NH-TDI—NH—COO—PETA.

According to another embodiment of the invention, the oligomer includesa crystallizable polyol-derived block in its structure. As used herein,a crystallizable polyol is one having a melting point of greater thanabout 0° C. Examples of crystallizable polyols includepoly(tetramethylene oxide), available as TERATHANE from E. I. duPont deNemours and Company; and poly(caprolactone) diol. One example of asuitable class of oligomers for use in the curable compositions of thepresent invention has the average structureCAP—OOC—NH—R_(I)—NH—[COO—R_(X)—OOC—NH—R_(I)—NH]_(w)—COO—CAPwhere w is greater than zero, CAP is a capping moiety having a reactiveterminus, and R_(X) includes at least one crystallizable polyol-derivedmoiety. Examples of average structures of oligomers havingcrystallizable polyol-derived moieties includeCLA-OOC—NH—H12MDI—NH—COO-T₍₁₀₀₀₎—OOC—NH—H12MDI—NH—COO—CLA;TMPPO[OOC—NH—IPDI—NH—COO-T₍₆₅₀₎—OOC—NH—IPDI—NH—COO—HEA]₃; and[HEA-OOC—NH—H12MDI—NH—COO-EO8BPA-OOC—NH—H12MDI—NH—COO]₂T₍₁₀₀₀₎,where EO8BPA has the average structure

and T₍₁₀₀₀₎ has an M_(n)˜1000 Daltons and the average structure—(CH₂CH₂CH₂CH₂O)_(u)(CH₂CH₂CH₂CH₂)—. T₍₆₅₀₎ has an M_(n)˜650 Daltons,and a structure analogous to that of T₍₁₀₀₀₎. The skilled artisan willrecognize that other combinations of CAP, R_(I), and R_(X) can be usedin the oligomers of this class.

According to another embodiment of the invention, the oligomer includesrigid subunits in its structure. Desirably, the rigid subunits are inthe polyol-derived portion of the oligomer. Examples of rigid subunitsinclude cyclic moieties such as

One example of a suitable class of oligomers for use in the curablecompositions of the present invention has the average structureCAP—OOC—NH—R_(I)—NH—[COO—R_(L)—OOC—NH—R_(I)—NH]_(w)—COO—CAPwhere w is greater than zero, CAP is a capping moiety having a reactiveterminus, and R_(L) includes at least one cyclic rigid moiety. Forexample, R_(L) may include the moiety —(R₄O)_(v)—R₅—(OR₄)_(v), where R₅is a rigid cyclic subunit, R₄ is ethylene, propylene, or butylene, and vranges from 0 to 7. Examples of average structures of oligomers havingrigid subunits include[HEA-OOC—NH—H12MDI—NH—COO—PO2BPA-OOC—NH]₂H12MDI;[HEA-OOC—NH—H12MDI—NH—COO-EO8BPA-OOC—NH—H12MDI—NH—COO]₂T₍₁₀₀₀₎;[HEA-OOC—NH—H12MDI—NH—COO—BPA-OOC—NH—H12MDI—NH—COO]₂PPG₍₄₂₅₎;[HEA-OOC—NH-TDI—NH—COO—BPA-OOC—NH-TDI—NH—COO]₂PPG₍₄₂₅₎;[HEA-OOC—NH—IPDI—NH—COO—BPA-OOC—NH]₂IPDI;[HEA-OOC—NH-TDI—NH—COO—BPA-OOC—NH]₂TDI;[HEA-OOC—NH—H12MDI—NH—COO—BPA-OOC—NH]₂H12MDI;[HEA-OOC—NH-TDI—NH—COO—CHDM-OOC—NH]₂TDI; and[PETA-OOC—NH-TDI—NH—COO—PO2BPA-OOC—NH]₂TDI,where PO2BPA has the average structure

T₍₁₀₀₀₎ has an M_(n)˜1000 Daltons and the average structure—(CH₂CH₂CH₂CH₂O)_(u)(CH₂CH₂CH₂CH₂)—; and PPG₍₄₂₅₎ has an M_(n)˜425Daltons and an average structure —(CHCH₃CH₂O)_(s)(CHCH₃CH₂)—. As theskilled artisan will appreciate, other combinations of CAP, R_(I), andR_(L) can be used in the oligomers of the present invention.

According to another embodiment of the invention, the oligomer includesboth rigid polyol-derived subunits and multiple functionality. Oneexample of a suitable class of oligomers for use in the curablecompositions of the present invention has the average structureR_(M)[OOC—NH—R_(I)—NH—(COO—R_(L)—OOC—NH—R_(I)—NH)_(w)—COO—CAP]_(n),where w is greater than zero, n is greater than 2.2, CAP is a cappingmoiety having a reactive terminus, and R_(L) includes at least onecyclic rigid moiety. Examples of average structures of this class ofoligomers includeGlyPO₍₇₂₅₎[OOC—NH—IPDI—NH—COO—BPA-OOC—NH—IPDI—NH—COO—HEA]₃;GlyPO₍₇₂₅₎[OOC—NH—H12MDI—NH—COO—BPA-OOC—NH—H12MDI—NH—COO—HEA]₃;GlyPO₍₇₂₅₎[OOC—NH-TDI—NH—COO—BPA-OOC—NH-TDI—NH—COO—HEA]₃;GlyPO₍₇₂₅₎[OOC—NH-TDI—(NH—COO—BPA-OOC—NH-TDI)₂—NH—COO—HEA]₃;GlyPO₍₇₂₅₎[OOC—NH-TDI—NH—COO—CHDM-OOC—NH-TDI—NH—COO—HEA]₃;GlyPO₍₇₂₅₎[OOC—NH-TDI—NH—COO—BPA-OOC—NH-TDI—NH—COO—CLA]₃;GlyPO₍₁₅₀₀₎[OOC—NH-TDI—NH—COO—BPA-OOC—NH-TDI—NH—COO—HEA]₃;PertPO₍₄₂₆₎[OOC—NH—IPDI—NH—COO—BPA-OOC—NH—IPDI—NH—COO—HEA]₄;PertPO₍₄₂₆₎[OOC—NH-TDI—NH—COO—BPA-OOC—NH-TDI—NH—COO—HEA]₄;PertPO₍₄₂₆₎[OOC—NH-TDI—(NH—COO—BPA-OOC—NH-TDI)₂—NH—COO—HEA]₄; andTMPPO[OOC—NH-TDI—NH—COO—BPA-OOC—NH-TDI—NH—COO—HEA]₃,where GlyPO₍₁₅₀₀₎ is a is a propoxylated glyceryl moiety having anM_(n)˜1500 Daltons. As the skilled artisan will appreciate, othercombinations of CAP, R_(I), R_(M) and R_(L) can be used in the oligomersof the present invention.

The skilled artisan may use other conventional oligomers in the curablecompositions of the present invention. For example, the oligomer may bethe capped product of the reaction of a dihydric polyether, polyester,or polycarbonate with an aliphatic or aromatic diisocyanate. When it isdesirable to provide increased moisture resistance, the skilled artisanmay use oligomers based on nonpolar diols, such as saturated aliphaticdiols. Examples of commercially available oligomers suitable for use inthe curable compositions of the present invention include BR301 andKWS4131, from Bomar Specialty Co.; RCC12-892 and RCC13-572, from CognisCorp; PHOTOMER 6010, from Cognis Corp; and EBECRYL 8800, 4883, 8804,8807, 8402, and 284, from UCB Radcure.

The curable compositions of the present invention also include one ormore monomers having reactive termini selected to react with thereactive termini of the oligomer. In general, individual monomerscapable of greater than about 80% conversion are more desirable thanthose having lower conversion rates. The degree to which monomers havinglow conversion rates can be introduced into the curable compositiondepends upon the particular requirements of the desired cured polymericmaterial. Typically, higher conversion rates will yield stronger curedproducts.

Suitable polyfunctional ethylenically unsaturated monomers for use inthe curable compositions of the present invention include, withoutlimitation, alkoxylated bisphenol A diacrylates such as ethoxylatedbisphenol A diacrylate with ethoxylation being 2 or greater, preferablyranging from 2 to about 30, and propoxylated bisphenol A diacrylate withpropoxylation being 2 or greater, preferably ranging from 2 to about 30(e.g., PHOTOMER 4025 and PHOTOMER 4028, available from Cognis Corp.(Ambler, Pa.)); methylolpropane polyacrylates with and withoutalkoxylation such as ethoxylated trimethylolpropane triacrylate withethoxylation being 3 or greater, preferably ranging from 3 to about 30(e.g., PHOTOMER 4149, Cognis Corp., and SR499, Sartomer Company, Inc.),propoxylated trimethylolpropane triacrylate with propoxylation being 3or greater, preferably ranging from 3 to 30 (e.g., PHOTOMER 4072, CognisCorp.), and ditrimethylolpropane tetraacrylate (e.g., PHOTOMER 4355,Cognis Corp.); alkoxylated glyceryl triacrylates such as propoxylatedglyceryl triacrylate with propoxylation being 3 or greater (e.g.,PHOTOMER 4096, Cognis Corp.); erythritol polyacrylates with and withoutalkoxylation, such as pentaerythritol tetraacrylate (e.g., SR295,available from Sartomer Company, Inc. (Westchester, Pa.)), ethoxylatedpentaerythritol tetraacrylate (e.g., SR494, Sartomer Company, Inc.), anddipentaerythritol pentaacrylate (e.g., PHOTOMER 4399, Cognis Corp., andSR399, Sartomer Company, Inc.); isocyanurate polyacrylates formed byreacting an appropriate cyanuric acid with an acrylic acid or acryloylchloride, such as tris(2-hydroxyethyl) isocyanurate triacrylate (e.g.,SR368, Sartomer Company, Inc.) and tris(2-hydroxyethyl) isocyanuratediacrylate; alcohol polyacrylates with and without alkoxylation such ascyclohexane dimethanol diacrylate (e.g., CD406, Sartomer Company, Inc.)and ethoxylated polyethylene glycol diacrylate with ethoxylation being 2or greater, preferably ranging from about 2 to 30; epoxy acrylatesformed by adding acrylate to bisphenol A diglycidylether and the like(e.g., PHOTOMER 3016, Cognis Corp.); and single and multi-ring cyclicaromatic or non-aromatic polyacrylates such as tricyclodecane dimethanoldiacrylate, dicyclopentadiene diacrylate and dicyclopentane diacrylate.Bisphenol A-based monomers are especially desirable for use in thecurable compositions of the present invention.

It may be desirable to include a polyfunctional thiol monomer in thecurable compositions of the present invention. A polyfunctional thiolmonomer can participate in the polymerization through free radicalthiol-ene reactions, and will provide a polymer network cross-linkedwith thioether moieties. Desirably, the polyfunctional thiol has a thiolfunctionality of at least about 3 thiols/molecule. Examples of suitablepolyfunctional thiols include pentaerythritoltetrakis(3-mercaptopropionate); trimethylolpropanetris(3-mercaptopropionate); and CAPCURE LOF, available from Cognis. Thepolyfunctional thiol monomer is desirably present in the curablecomposition in an amount of between about 2 wt % and about 20 wt %. Incertain desirable curable compositions, the polyfunctional thiol monomeris present in an amount of between about 5 wt % and about 15 wt %.

It may also be desirable to use certain amounts of monofunctionalethylenically unsaturated monomers, which can be introduced to influencethe degree to which the cured product absorbs water, adheres to othercoating materials, or behaves under stress. Exemplary monofunctionalethylenically unsaturated monomers include, without limitation,hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, and 2-hydroxybutyl acrylate; long- and short-chain alkylacrylates such as methyl acrylate, ethyl acrylate, propyl acrylate,isopropyl acrylate, butyl acrylate, amyl acrylate, isobutyl acrylate,t-butyl acrylate, pentyl acrylate, isoamyl acrylate, hexyl acrylate,heptyl acrylate, octyl acrylate, isooctyl acrylate, 2-ethylhexylacrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, undecylacrylate, dodecyl acrylate, lauryl acrylate, octadecyl acrylate, andstearyl acrylate; aminoalkyl acrylates such as dimethylaminoethylacrylate, diethylaminoethyl acrylate, and 7-amino-3,7-dimethyloctylacrylate; alkoxyalkyl acrylates such as butoxylethyl acrylate,phenoxyethyl acrylate (e.g., SR339, Sartomer Company, Inc.), andethoxyethoxyethyl acrylate; single and multi-ring cyclic aromatic ornon-aromatic acrylates such as cyclohexyl acrylate, benzyl acrylate,dicyclopentadiene acrylate, dicyclopentanyl acrylate, tricyclodecanylacrylate, bornyl acrylate, isobornyl acrylate (e.g., SR506, SartomerCompany, Inc.), tetrahydrofurfuryl acrylate (e.g., SR285, SartomerCompany, Inc.), caprolactone acrylate (e.g., SR495, Sartomer Company,Inc.), and acryloylmorpholine; alcohol-based acrylates such aspolyethylene glycol monoacrylate, polypropylene glycol monoacrylate,methoxyethylene glycol acrylate, methoxypolypropylene glycol acrylate,methoxypolyethylene glycol acrylate, ethoxydiethylene glycol acrylate,and various alkoxylated alkylphenol acrylates such as ethoxylated(4)nonylphenol acrylate (e.g., PHOTOMER 4003, Cognis Corp.); acrylamidessuch as diacetone acrylamide, isobutoxymethyl acrylamide,N,N′-dimethyl-aminopropyl acrylamide, N,N-dimethyl acrylamide,N,N-diethyl acrylamide, and t-octyl acrylamide; vinylic compounds suchas N-vinylpyrrolidone and N-vinylcaprolactam; and acid esters such asmaleic acid esters and fumaric acid esters.

Most suitable monomers are either commercially available or readilysynthesized using reaction schemes known in the art. For example, mostof the above-listed monofunctional monomers can be synthesized byreacting an appropriate alcohol or amine with an acrylic acid oracryloyl chloride.

According to one embodiment of the present invention, the total oligomercontent of the curable composition is less than about 25%. In especiallydesirable embodiments of the invention, the total oligomer content isless than about 15% In desirable embodiments of the present invention,the total monomer content of the curable composition is greater thanabout 65%. In especially desirable embodiments of the invention, themonomer content of the curable composition is greater than about 75%.Use of relatively low amounts of oligomer allows the skilled artisan toeasily formulate curable compositions having a desirable viscosity. Asthe oligomer is typically a more expensive component of the composition,minimization of the amount of oligomer allows the skilled artisan toreduce the cost of the curable composition, as well as the cost ofarticles, such as optical fibers, coated therewith. Secondary coatingcompositions having low oligomer content are described in more detail inU.S. patent application Ser. No. 09/722,895, which is incorporatedherein by reference in its entirety. The oligomer is desirable presentin the curable composition in a concentration of at least about 1 wt %.

The curable compositions of the present invention may also include apolymerization initiator. The initiator is desirably present in anamount effective to initiate polymerization of the curable composition.Desirable curable compositions of the present invention are adapted tobe cured by actinic radiation, and include one or more photoinitiators.For most (meth)acrylate-based curable compositions, conventionalphotoinitiators, such as ketonic and/or phosphine-oxide basedinitiators, may be used. Generally, the total photoinitiator content ofthe curable composition is between about 0.1 and about 10.0 weightpercent. More desirably, the total photoinitiator content of the curablecomposition is between about 1.0 and about 7.5 weight percent. Suitablephotoinitiators include, without limitation, 1-hydroxycyclohexylphenylketone (e.g., IRGACURE 184 available from Ciba Specialty Chemical(Tarrytown, N.Y.)), (2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (e.g., in commercial blends IRGACURE 1800, 1850, and1700, Ciba Specialty Chemical), 2,2-dimethoxyl-2-phenyl acetophenone(e.g., IRGACURE 651, Ciba Specialty Chemical),bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (e.g., IRGACURE 819,Ciba Specialty Chemical), (2,4,6-trimethylbenzoyl)diphenyl phosphineoxide (e.g., in commercial blend DAROCUR 4265, Ciba Specialty Chemical),2-hydroxy-2-methyl-1-phenylpropane-1-one (e.g., in commercial blendDAROCUR 4265, Ciba Specialty Chemical) and combinations thereof. It maybe desirable to use a combination of an α-hydroxy ketone photoinitiator(e.g., IRGACURE 184) with a bis(acyl)phosphine oxide photoinitator(e.g., IRGACURE 819) to provide both adequate surface cure and adequatecure of the bulk material. Curable compositions for use as secondarycoatings in optical fibers may be formulated with a photoinitator havingan absorption spectrum that does not completely overlap the absorptionspectrum of the photoinitiator used in the primary coating composition,as is described in U.S. patent application Ser. No. 10/086,109, which isincorporated herein by reference in its entirety. Other photoinitiatorsare continually being developed and used in coating compositions onglass fibers. Any suitable photoinitiator can be introduced intocompositions of the present invention.

In addition to the above-described components, the curable compositionsof the present invention can optionally include an additive or acombination of additives. Suitable additives include, withoutlimitation, antioxidants, catalysts, lubricants, low molecular weightnon-crosslinking resins, adhesion promoters, coupling agents, coloringagents, and stabilizers. Some additives can operate to control thepolymerization process, thereby affecting the physical properties (e.g.,modulus, glass transition temperature) of the polymerization productformed from the composition. Others can affect the integrity of thepolymerization product of the composition (e.g., protect againstde-polymerization or oxidative degradation). A desirable antioxidant isthiodiethylene bis(3,5-di-tert-butyl)-4-hydroxyhydrocinnamate, availableas IRGANOX 1035 from Ciba Specialty Chemical). A suitable adhesionpromoter is an acrylated acid adhesion promoter such as EBECRYL 170,available from UCB Radcure. Titanium and zirconium-based coupling agentsand optical brighteners such as those described in U.S. patentapplication Ser. Nos. 09/726,002 and 09/747,480, each of which isincorporated herein by reference in its entirety, may also be used inthe curable compositions of the present invention. Optical brightenerssuch as UVITEX OB, available from Ciba may also be used in the curablecompositions of the present invention.

Other suitable materials for use in secondary coating materials, as wellas considerations related to selection of these materials, are wellknown in the art and are described in U.S. Pat. Nos. 4,962,992 and5,104,433 to Chapin, which are hereby incorporated herein by referencein their entirety. Various additives that enhance one or more propertiesof the coating can also be present, including the above-mentionedadditives incorporated in the compositions of the present invention.

The curable compositions of the present invention may be cured to yieldcured polymeric materials having substantially homogeneous morphologies.AFM phase maps for three cured polymeric materials are shown in FIG. 3.These AFM phase maps were generated using a Digital InstrumentsNanoscope, with a scan size of 1 μm, and a scan rate of 1.485 Hz. Thetop AFM phase map exhibits a substantially inhomogeneous morphology,having large (>30 nm long) bright white grains in a dark background.This AFM phase map is for a cured polymeric material havingphase-segregated hard (white) regions. The bottom two AFM phase maps arefor cured polymeric materials of the present invention (curablecompositions 36 and 2, respectively, of Example 2, below). These AFMphase maps have only miniscule grayish grains, indicating asubstantially homogeneous morphology, with little (if any) phasesegregation.

Another embodiment of the present invention relates to a method ofmaking an optical fiber including the secondary coating describedhereinabove. This method can generally be performed by standard methodswith the use of a composition of the present invention. Briefly, theprocess involves fabricating the glass fiber (using methods familiar tothe skilled artisan), applying a primary coating composition to theglass fiber, polymerizing the primary coating composition to form theprimary coating material, applying the curable composition describedhereinabove to the coated glass fiber, and polymerizing the curablecomposition to form the cured polymeric material as the secondarycoating of the optical fiber. Optionally, the secondary coatingcomposition can be applied to the coated fiber before polymerizing theprimary coating composition, in which case only a single polymerizationstep is employed.

The primary and secondary coating compositions are coated on a glassfiber using conventional processes, for example, on a draw tower. It iswell known to draw glass fibers from a specially prepared, cylindricalpreform which has been locally and symmetrically heated to atemperature, e.g., of about 2000° C. As the preform is heated, such asby feeding the preform into and through a furnace, a glass fiber isdrawn from the molten material. One or more coating compositions areapplied to the glass fiber after it has been drawn from the preform,preferably immediately after cooling. The coating compositions are thencured to produce the coated optical fiber. The method of curing can bethermal, chemical, or radiation induced, such as by exposing the applied(and un-cured) coating composition on the glass fiber to ultravioletlight, actinic radiation, microwave radiation, or electron beam,depending upon the nature of the coating composition(s) andpolymerization initiator being employed. It is frequently advantageousto apply both a primary coating composition and any secondary coatingcompositions in sequence following the draw process. One method ofapplying dual layers of coating compositions to a moving glass fiber isdisclosed in U.S. Pat. No. 4,474,830 to Taylor, which is herebyincorporated by reference in its entirety. Another method for applyingdual layers of coating compositions onto a glass fiber is disclosed inU.S. Pat. No. 4,581,165 to Rannell et al., which is hereby incorporatedby reference in its entirety. Of course, the primary coating compositioncan be applied and cured to form the primary coating material, then thecurable composition described hereinabove can be applied and cured toform the cured polymeric material of the secondary coating.

Still another embodiment of the present invention relates to an opticalfiber ribbon. The ribbon includes a plurality of optical fibers and amatrix encapsulating the plurality of optical fibers. The matrix is thecured product of a curable composition of the present inventiondisclosed hereinabove.

One embodiment of a ribbon of the present invention is illustrated inFIG. 4. As shown therein, fiber optic ribbon 90 of the present inventionincludes a plurality of single or multi-layered optical fibers 92substantially aligned relative to one another in a substantially planarrelationship and encapsulated by matrix 94. The skilled artisan willappreciate that the optical fibers 92 may include a dual-layer coatingsystem (for example, the primary and secondary coatings describedhereinabove), and may be colored with a marking ink. It is desirablethat optical fibers 92 are not displaced from a common plane by adistance of more than about one-half the diameter thereof. Bysubstantially aligned, it is intended that the optical fibers 92 aregenerally parallel with other optical fibers along the length of thefiber optic ribbon 90. In FIG. 4, the fiber optic ribbon 90 containssixteen (16) optical fibers 92; however, it should be apparent to thoseskilled in the art that any number of optical fibers 92 (e.g., two ormore) may be employed to form fiber optic ribbon 90 disposed for aparticular use.

The optical fibers in fiber optic ribbons of the present invention maybe encapsulated by the matrix 94 in any known configuration (e.g.,edge-bonded ribbon, thin-encapsulated ribbon, thick-encapsulated ribbon,or multi-layer ribbon) by conventional methods of making fiber opticribbons.

The fiber optic ribbon may be prepared by conventional methods using thecurable composition of the present invention to form the matrixmaterial. For example, upon alignment of a plurality of substantiallyplanar optical fibers, the composition of the present invention can beapplied and cured according to the methods of preparing optical fiberribbons as described in U.S. Pat. No. 4,752,112 to Mayr and U.S. Pat.No. 5,486,378 to Oestreich et al., which are hereby incorporated byreference in their entirety.

The curable compositions of the present invention may also beadvantageously used in the formulation of marking inks for opticalfibers. As such, according to another embodiment of the presentinvention, a coated optical fiber includes an optical fiber; a coatingsystem encapsulating the optical fiber (such as the coating systemsdescribed hereinabove), and a marking ink deposited on the exterior ofthe coating system. For example, FIG. 5 shows a schematic view of amarked optical fiber 100 including a glass optical fiber 102; a coatingsystem including primary coating 104 and secondary coating 106; and amarking ink 108. The marking ink is the cured product of a curablecomposition of the present invention disclosed hereinabove. A markingink is typically formed as a thin layer of a colored coating on theouter surface of a secondary coating of an optical fiber. Pigmentsand/or dyes may be added by the skilled artisan to the curablecompositions of the present invention to provide a suitable marking ink.It may be desirable to include a titanate or zirconate coupling agent inthe marking ink curable composition, as described in U.S. Pat. No.6,553,169, which is incorporated herein by reference in its entirety.

The curable compositions and cured polymeric materials of the presentinvention have been described hereinabove in conjunction with asecondary coating of an optical fiber. However, the skilled artisan willappreciate that the curable compositions and cured polymeric materialsdescribed herein may be useful in other coating applications requiringvery hard, tough coatings. As such, another embodiment of the presentinvention relates to a cured polymeric material having a Young's modulusof at least about 1200 MPa and a fracture toughness of at least about0.7 MPa/m^(1/2). The cured polymeric material may have other desirableproperties described hereinabove with reference to the cured polymericmaterial of the secondary coating of the optical fiber. For example, thecured polymeric material may have a ductility of at least about 38 μm.The cured polymeric material may be the cured reaction product of thecurable compositions of the present invention, described hereinabove.

In order to couple an optical fiber to a device or to another opticalfiber, it is typically necessary to strip the dual coating system off ofa portion of the optical fiber. The curable compositions of the presentinvention may be useful in recoating a stripped optical fiber, forexample, at a splice joint or splice junction. The polymeric coating maybe any of the secondary coatings described hereinabove, and may beformed using any of the curable compositions described hereinabove. Thesplice-junction coating is preferably between about 40 and about 260microns in thickness, more preferably between about 40 and 125 microns.

More specifically, and with reference to FIG. 6, the optical fiber 200to be formed upon splicing is recoated at a splice junction where firstand second optical fiber segments 201, 202 are joined together. As notedabove, each of the segments includes an optical fiber having at leastone coating 203, 204 thereon, which at least one coating has beenremoved from an end section 201′, 202′ thereof. The end sections ofthese first and second optical fiber segments are spliced togetherend-to-end, which is known as a butt splice. After creating the splicejunction (i.e., by placing the two butt ends together), the splicejunction is coated with a coating composition so as to encapsulate theend sections of the first and second segments and contact the coatingsof the first and second optical fiber segments (i.e., at the coatingsurface exposed when they were stripped). The coating composition isthen cured, forming the recoat 205, to provide a re-coated optical fiber200 of the present invention.

According to one embodiment of the present invention, the re-coatedoptical fiber contains a cured splice-junction coating (i.e., a recoat)having a Young's modulus of at least about 1200 MPa. As described above,coatings having higher Young's modulus values are even more preferredfor use as a recoat. Preferably, the recoat also has a fracturetoughness of at least about 0.7 MPa·m^(1/2).

EXAMPLES

The present invention is further described by the following non-limitingexamples.

Example 1 Oligomer Synthesis

Example oligomers 1–33 were synthesized as described below. Unlessotherwise specified, processes conducted under vacuum were conducted atpressures on the order of 1 Torr. The dibutyltin dilaurate,4-methoxyphenol (MEHQ), phenothiazine and2,6-di-tert-butyl-4-methylphenol (BHT) were purchased from AldrichChemical Co. Polyols used to prepare oligomers were generally heated at40–50° C. for 12 h under vacuum to remove traces of water prior to use.All other materials were used as received.

Urethane acrylate oligomer 1 with the average structureCLA-OOC—NH—H12MDI—NH—COO—CLA was prepared by mixing 35.0 g (0.133 mole)DESMODUR W (H12MDI(NCO)₂, Bayer) with 91.8 g (0.266 mole) caprolactoneacrylate (Sartomer, SR495) along with 190 mg dibutlyltin dilaurate and190 mg BHT at 20° C. The mixture was stirred at this temperature for 1.5h, and then was heated at 75–85° C. for 3 h.

Urethane acrylate oligomer 2 with the average structureGlyPO₍₇₂₅₎[OOC—NH—H12MDI—NH—COO—HEA]₃ was prepared by slow addition of75.2 g (0.648 mole) 2-hydroxyethyl acrylate (Aldrich) to an ice-cooledmixture of 170.0 g (0.648 mole) DESMODUR W containing 611 mg BHT and 611mg dibutyltin dilaurate. Following the addition, the mixture was heatedat 75–80° C. for 1 h. The mixture was cooled to less than 65° C. and156.60 g (0.216 mole) of propoxylated glycerol (M_(n)=725, Aldrich) wasadded over 1.5 h. The mixture was heated at 75–80° C. for 1 h tocomplete the reaction.

Urethane acrylate oligomer 8 with the average structureUMB2005[OOC—NH—H12MDI—NH—COO—HEA]_(2.4) was prepared by slow addition of11.07 g (0.0.095 mole) 2-hydroxyethyl acrylate (Aldrich) to anice-cooled mixture of 25.0 g (0.095 mole) DESMODUR W containing 144 mgBHT and 144 mg dibutyltin dilaurate. Following the addition, the mixturewas heated at 75–80° C. for 1 h. The mixture was cooled to less than 65°C. and 60.13 g (0.023 mole) of UMB2005 (Esprix Technologies, hydroxylfunctional [2.4 equivalents per chain] poly(butylacrylate) with M_(n)about 2600) was added over 45 min. The mixture was heated at 75–80° C.for 1 h to complete the reaction.

Urethane acrylate oligomer 9 with the average structureTMPPO[OOC—NH—IPDI—NH—COO—PPG₍₄₂₅₎—OOC—NH—IPDI—NH—COO—HEA]₃ was preparedby initial addition over 1.5 h of 40.0 g (0.094 mole) of poly(propyleneglycol) (Aldrich, M_(n)=425) to an ice cooled mixture of 41.84 g (0.188mole) of isophorone diisocyanate (Aldrich) containing 150 mg of BHT(Aldrich) stabilizer and 150 mg of dibutyltin dilaurate (Aldrich).Following the addition the mixture was heated at 75–80° C. for 2 h. Theheat source was removed and the mixture was diluted with 102.4 gPHOTOMER 4028 (ethoxylated (4) bisphenol A diacrylate, Cognis). When thetemperature of the mixture was less than 55° C. 10.93 g (0.094 mole) of2-hydroxyethyl acrylate (Aldrich) was added over 15 min. The mixture washeated at 75–80° C. for 2 h and was then cooled to less than 70° C. when9.66 g (0.031 mole) of propoxylated (1PO/OH) trimethylolpropane(Aldrich, M_(n)=308) was added over 10 min. The mixture was heated at75–80° C. for 2.5 h to complete the reaction. The end product was a 1:1mixture of oligomer 9 with PHOTOMER 4028.

Urethane acrylate oligomer 11 with the average structurePETA-OOC—NH—TDI—NH—COO—PETA was prepared by mixing 61.7 g (0.207 mole)pentaerythritol triacrylate along with 120 mg MEHQ, and 120 mgphenothiazine (Aldrich) and heating this under vacuum at 75–80° C. for1.5 h. The vacuum was released and the mixture was placed under nitrogenand cooled to less than 20° C. when 18.0 g (0.103 mole) toluenediisocyanate was added over 5 min, followed by 160 mg dibutyltindilaurate. The mixture was then heated at 75–80° C. for 2.5 h tocomplete the reaction.

Urethane acrylate oligomer 14 with the average structure[HEA-OOC—NH-TDI—NH—COO—PO2BPA-OOC—NH]₂TDI was prepared by mixing 40.0 g(0.116 mole) propoxylated (1 PO/OH) bisphenol A (Aldrich) and 130 mg BHTand heating this under vacuum at 75–80° C. for 1 h. The vacuum wasremoved and 83.85 g PHOTOMER 4028 was added. The mixture was cooled toless than 20° C. and 30.35 g (0.174 mole) toluene diisocyanate (Aldrich,mixture of 2,4 and 2,6 isomers) was added, followed by 130 mg dibutyltindilaurate. Stirring at 20° C. was continued for 1 h. The mixture wasthen heated at 75–80° C. for 1 h. The mixture was allowed to cool toless than 70° C. and 13.50 g (0.116 mole) hydroxyethyl acrylate wasadded over 15 min. The mixture was heated at 75–80° C. for an additional2 h to complete the reaction. The end product was a 1:1 mixture ofoligomer 14 with PHOTOMER 4028.

Urethane acrylate oligomer 15 with the average structure[HEA-OOC—NH—H12MDI—NH—COO-EO8BPA-OOC—NH—H12MDI—NH—COO]₂T₍₁₀₀₀₎ wasprepared by mixing 60.0 g (0.103 mole) ethoxylated (4 EO/OH) bisphenol A(Aldrich) and 260 mg BHT and heating this under vacuum at 75–80° C. for1 h. The vacuum was removed and 178.0 g PHOTOMER 4028 was added. Themixture was cooled to less than 20° C. and 54.3 g (0.207 mole) DESMODURW was added, followed by 260 mg dibutyltin dilaurate. Stirring at 20° C.was continued for 20 min. The mixture was then heated at 75–80° C. for1.5 h. The mixture was allowed to cool to less than 70° C. and 51.7 g(0.052 mole) of TERATHANE 1000 (Aldrich) was added over 20 min. Themixture was heated at 75–80° C. for 1.5 h and then 12.0 g (0.103 mole)2-hydroxyethyl acrylate was added, followed by additional heating at75–80° C. for 1.5 h to complete the reaction. The end product was a 1:1mixture of oligomer 15 with PHOTOMER 4028.

Urethane acrylate oligomer 23 with the average structureGlyPO₍₇₂₅₎[OOC—NH—IPDI—NH—COO—BPA-OOC—NH—IPDI—NH—COO—HEA]₃ was preparedby initially heating a mixture of 67.8 g PHOTOMER 4028, 15.0 g (0.066mole) bisphenol A and 100 mg of MEHQ stabilizer at 75–80° C. undervacuum (1 mm) for 1 h. The vacuum was released and the mixture wasplaced under nitrogen and cooled to less than 20° C. when 29.25 g (0.132mole) of isophorone diisocyanate was added, followed by 100 mg ofdibutyltin dilaurate. The mixture was heated at 75–80° C. for 1.5 h andwas then cooled to less than 65° C. when 7.64 g (0.066 mole) of2-hydroxyethyl acrylate was added over 5 min. The mixture was heated at75–80° C. for 1.5 h and then cooled again to less than 65° C. followedby addition of 15.90 g (0.022 mole) glycerol propoxylate (Aldrich,M_(n)=725) over 5 min. The mixture was heated at 75–80° C. for 2 h tocomplete the reaction. The end product was a 1:1 mixture of oligomer 23with PHOTOMER 4028.

Urethane acrylate oligomers 3–7, 10, 12, 13, 16–22 and 24–34 wereprepared using procedures substantially similar to those describedabove. Structures for these oligomers are given in Table 3; an asteriskafter the oligomer number denotes that the oligomer was prepared as a1:1 mixture of the oligomer with PHOTOMER 4028.

TABLE 3 Oligomer Structure  3 GlyPO₍₇₂₅₎[OOC—NH-H12MDI-NH—COO-CLA]₃  4GlyPO₍₇₂₅₎[OOC—NH-TMXDI-NH—COO-CLA]₃  5GlyPO₍₇₂₅₎[OOC—NH-TDI-NH—COO-CLA]₃  6GlyPO₍₇₂₅₎[OOC—NH-TDI-NH—COO-PETA]₃  7PertPO₍₄₂₆₎[OOC—NH-H12MDI-NH—COO-CLA]₄ 10TMPPO[OOC—NH-IPDI-NH—COO-T₍₆₅₀₎-OOC—NH- IPDI-NH—COO-HEA]₃ 12CLA-OOC—NH-H12MDI-NH—COO-T₍₁₀₀₀₎-OOC—NH- H12MDI-NH—COO-CLA 13*[HEA-OOC—NH-H12MDI-NH—COO-PO2BPA-OOC— NH]₂H12MDI 16*[HEA-OOC—NH-H12MDI-NH—COO-BPA-OOC—NH- H12MDI-NH—COO]₂PPG₍₄₂₅₎ 17*[HEA-OOC—NH-TDI-NH—COO-BPA-OOC—NH-TDI- NH—COO]₂PPG₍₄₂₅₎ 18*[HEA-OOC—NH-IPDI-NH—COO-BPA-OOC—NH]₂IPDI 19*[HEA-OOC—NH-TDI-NH—COO-BPA-OOC—NH]₂TDI 20*[HEA-OOC—NH-H12MDI-NH—COO-BPA-OOC—NH]₂ H12MDI 21*[HEA-OOC—NH-TDI-NH—COO-CHDM-OOC—NH]₂TDI 22*[PETA-OOC—NH-TDI-NH—COO-PO2BPA-OOC—NH]₂ TDI 24*GlyPO₍₇₂₅₎[OOC—NH-H12MDI-NH—COO-BPA- OOC—NH-H12MDI-NH—COO-HEA]₃ 25*GlyPO₍₇₂₅₎[OOC—NH-TDI-NH—COO-BPA-OOC— NH-TDI-NH—COO-HEA]₃ 26*GlyPO₍₇₂₅₎[OOC—NH-TDI-(NH—COO-BPA-OOC—NH- TDI)₂-NH—COO-HEA]₃ 27*GlyPO₍₇₂₅₎[OOC—NH-TDI-NH—COO-CHDM-OOC— NH-TDI-NH—COO-HEA]₃ 28*GlyPO₍₇₂₅₎[OOC—NH-TDI-NH—COO-BPA-OOC— NH-TDI-NH—COO-CLA]₃ 29*GlyPO₍₁₅₀₀₎[OOC—NH-TDI-NH—COO-BPA-OOC— NH-TDI-NH—COO-HEA]₃ 30*PertPO₍₄₂₆₎[OOC—NH-IPDI-NH—COO-BPA-OOC— NH-IPDI-NH—COO-HEA]₄ 31*PertPO₍₄₂₆₎[OOC—NH-TDI-NH—COO-BPA-OOC— NH-TDI-NH—COO-HEA]₄ 32*PertPO₍₄₂₆₎[OOC—NH-TDI-(NH—COO-BPA-OOC— NH-TDI)₂-NH—COO-HEA]₄ 33*TMPPO[OOC—NH-TDI-NH—COO-BPA-OOC—NH- TDI-NH—COO-HEA]₃ 34*[HEA-OOC—NH-TDI-NH—COO-PO2NPG-OOC— NH]₂TDI

Example 2 Formulation of Curable Compositions

Curable compositions 1–37 were formulated in a jacketed beaker heated to70° C. using a high-speed mixer. In each case, the components wereweighed into the jacketed beaker using a balance and allowed to mixuntil the solid components were thoroughly dissolved and the mixtureappeared homogeneous. Curable compositions are formulated such that theamounts of oligomer, monomer, and photoinitiator total 100 wt %; otheradditives such as antioxidant are added to the total mixture in units ofpph. For oligomers which are provided as a 1:1 mixture of oligomer andmonomer, only the oligomeric component is counted as oligomer. Forexample, a curable composition made with 20% of a 1:1 mixture ofoligomer 9 with PHOTOMER 4028 would have 10% oligomer. Table 4 lists thecompositional details for each composition. Each composition alsoincludes 1.5% IRGACURE 184, 1.5% IRGACURE 819, and 0.5 pph IRGANOX 1035,each of which is available from Ciba. BLANKOPHOR KLA is a commerciallyavailable optical brightener.

TABLE 4 Curable Composition 1 10% Oligomer 1; 82% PHOTOMER 4028; 5%PHOTOMER 3016; 0.1 pph BLANKOPHOR KLA 2 10% Oligomer 2; 82% PHOTOMER4028; 5% PHOTOMER 3016; 0.1 pph BLANKOPHOR KLA 3 10% Oligomer 3; 82%PHOTOMER 4028; 5% PHOTOMER 3016; 0.1 pph BLANKOPHOR KLA 4 10% Oligomer4; 87% PHOTOMER 4028; 5%; 0.1 pph BLANKOPHOR KLA 5 10% Oligomer 5; 87%PHOTOMER 4028; 5%; 0.1 pph BLANKOPHOR KLA 6 10% Oligomer 6; 82% PHOTOMER4028; 5% PHOTOMER 3016 7 20% Oligomer 7; 77% PHOTOMER 4028; 0.1 pphBLANKOPHOR KLA 8 10% Oligomer 8; 82% PHOTOMER 4028; 5% PHOTOMER 3016;0.1 pph BLANKOPHOR KLA 9 10% Oligomer 9; 82% PHOTOMER 4028; 5% PHOTOMER3016 10 10% Oligomer 10; 82% PHOTOMER 4028; 5% PHOTOMER 3016 11 10%Oligomer 11; 82% PHOTOMER 4028; 5% PHOTOMER 3016 12 10% Oligomer 12; 82%PHOTOMER 4028; 5% PHOTOMER 3016; 0.1 pph BLANKOPHOR KLA 13 10% Oligomer13; 82% PHOTOMER 4028; 5% PHOTOMER 3016; 0.1 pph BLANKOPHOR KLA 14 10%Oligomer 14; 82% PHOTOMER 4028; 5% PHOTOMER 3016; 0.1 pph BLANKOPHOR KLA15 10% Oligomer 15; 82% PHOTOMER 4028; 5% PHOTOMER 3016; 0.1 pphBLANKOPHOR KLA 16 10% Oligomer 16; 82% PHOTOMER 4028; 5% PHOTOMER 301617 10% Oligomer 17; 82% PHOTOMER 4028; 5% PHOTOMER 3016 18 10% Oligomer18; 82% PHOTOMER 4028; 5% PHOTOMER 3016 19 10% Oligomer 19; 82% PHOTOMER4028; 5% PHOTOMER 3016 20 10% Oligomer 20; 82% PHOTOMER 4028; 5%PHOTOMER 3016 21 10% Oligomer 21; 82% PHOTOMER 4028; 5% PHOTOMER 3016 2210% Oligomer 22; 82% PHOTOMER 4028; 5% PHOTOMER 3016 23 10% Oligomer 23;82% PHOTOMER 4028; 5% PHOTOMER 3016 24 10% Oligomer 24; 82% PHOTOMER4028; 5% PHOTOMER 3016 25 10% Oligomer 25; 82% PHOTOMER 4028; 5%PHOTOMER 3016 26 10% Oligomer 26; 82% PHOTOMER 4028; 5% PHOTOMER 3016 2710% Oligomer 27; 82% PHOTOMER 4028; 5% PHOTOMER 3016 28 10% Oligomer 28;82% PHOTOMER 4028; 5% PHOTOMER 3016 29 10% Oligomer 29; 82% PHOTOMER4028; 5% PHOTOMER 3016 30 10% Oligomer 30; 82% PHOTOMER 4028; 5%PHOTOMER 3016 31 10% Oligomer 31; 82% PHOTOMER 4028; 5% PHOTOMER 3016 3210% Oligomer 32; 82% PHOTOMER 4028; 5% PHOTOMER 3016 33 10% Oligomer 33;82% PHOTOMER 4028; 5% PHOTOMER 3016 34 10% Oligomer 34; 82% PHOTOMER4028; 5% PHOTOMER 3016 35 10% Oligomer 7; 82% PHOTOMER 4028; 5% PHOTOMER3016; 0.1 pph BLANKOPHOR KLA 36 20% PHOTOMER 6008; 77% PHOTOMER 4028 3720% PHOTOMER 6008; 67% PHOTOMER 4028; 10% pentaerythritol tetrakis(3-mercaptopropionate) 38 20% PHOTOMER 6008 Urethane acrylate 77%PHOTOMER 4028 Ethoxylated Bisphenol A diacrylate 1.5% IRGACURE 184Photoinitiator 1.5% IRGACURE 819 Photoinitiator 0.5 pph IRGANOX 1035Antioxidant 0.1 pph BLANKOPHOR KLA Additive 39 10% KWS 4131 urethaneacrylate, Bomar Specialties Co. (Winston, CN) 82% PHOTOMER 4028difunctional monomer, Cognis Corp. (Ambler, PA) 5% PHOTOMER 3016difunctional monomer, Cognis Corp. 1.5% IRGACURE 819 photoinitiator,Ciba Specialty Chemical (Tarrytown, NY) 1.5% IRGACURE 184photoinitiator, Ciba Specialty Chemical 0.5 pph IRGANOX 1035antioxidant, Ciba Specialty Chemical 40 20% PHOTOMER 6008 UrethaneAcrylate 57% PHOTOMER 4028 Ethoxylated Bisphenol A diacrylate 20%V-CAP/RC vinyl caprolactain 1.5% IRGACURE 184 photoinitiator 1.5%IRGACURE 819 photoinitiator 0.5 pph IRGANOX 1035 antioxidant 0.1 pphBLANKOPHOR KLA optical brightener (Bayer)

Example 3 Cured Polymer Material Properties

Curable compositions 1–37 of Example 2 were used to make rod samples fortensile testing. Rods were prepared by injecting the curablecompositions into TEFLON tubing with an inner diameter of about 0.025″.The samples were cured using a Fusion D bulb at a dose of about 2.6J/cm² (measured over a wavelength range of 225–424 nm by a Light Bugmodel IL390 from International Light). After curing, the TEFLON tubingwas stripped, leaving rod samples about 0.0225″ in diameter. The curedrods were allowed to condition overnight in a laboratory with acontrolled temperature of 23° C. and a controlled relative humidity of50%. Young's modulus, tensile strength, and percent elongation to breakwere measured for each material using a Sintech MTS Tensile Tester.Yield stress was measured at the same time as the other tensile data forcertain of the materials. The gauge length was 5.1 cm, and the testspeed was 2.5 cm/min. The reported data are averages of 10 samples, andthe reported uncertainties are standard deviations.

Curable compositions 1–35 of Example 2 were also used to make filmsamples for fracture toughness testing. Film samples were prepared bycasting the curable compositions glass plates using a 0.010″ draw downbar. The films were cured using a Fusion D bulb at a dose of about 1.4J/cm² (measured over a wavelength range of 225–424 nm by a Light Bugmodel IL390 from International Light). The cured films were allowed tocondition overnight in a laboratory with a controlled temperature of 23°C. and a controlled relative humidity of 50%. Fracture toughness K_(1C)was measured on the cured films using the method described hereinabove.Three samples at each of three different notch lengths were measured;the reported value and uncertainty are the mean and standard deviationfor all six trials. The ductility for many of the materials wascalculated from mean value of K_(1C) and yield stress as describedabove.

Table 5 shows tensile and fracture toughness data for the cured polymermaterials made by curing the curable compositions 1–37.

TABLE 5 Tensile Young's strength % Modulus K_(1C) Ductility Composition(MPa) Elongation (MPa) (MPa · m^(1/2)) (μm)  1 80.7 ± 8.3 58 ± 5 1942 ±37 0.898 ± 0.079  2 66.3 ± 6.5 42 ± 7 1915 ± 30 0.920 ± 0.089  3 80.5 ±8.7 55 ± 7 1934 ± 58 0.927 ± 0.066  4 68.8 ± 4.6 50 ± 5 1660 ± 95 0.860± 0.083  5 70.9 ± 5 55 ± 4 1729 ± 87 1.040 ± 0.114  6 68.3 ± 5.8 40 ± 52278 ± 89 1.315 ± 0.072 480  7 71.2 ± 4.4 70 ± 4 1472 ± 70 0.858 ± 0.086 8 67.1 ± 3.2 39 ± 3 2096 ± 57 1.005 ± 0.045  9 66.7 ± 5.9 46 ± 3 1990 ±41 1.052 ± 0.053 10 55.6 ± 6.1 72 ± 10 1654 ± 28 1.061 ± 0.092 543 1174.1 ± 3.6 33 ± 4 2472 ± 41 1.054 ± 0.110 254 12 65.9 ± 5.4 59 ± 5 1437± 64 0.774 ± 0.067 13 73.8 ± 3.2 59 ± 4 1979 ± 44 0.860 ± 0.083 14 69.2± 8.0 38 ± 6 2502 ± 286 1.302 ± 0.086 15 67.6 ± 6.4 56 ± 7 1722 ± 520.880 ± 0.063 16 67.0 ± 3.7 41 ± 7 2247 ± 59 1.418 ± 0.059 500 17 63.4 ±2.4 35 ± 6 2265 ± 78 1.363 ± 0.079 474 18 68.3 ± 4.9 45 ± 4 2340 ± 771.398 ± 0.065 477 19 64.5 ± 2.4 41 ± 4 2317 ± 53 1.388 ± 0.075 500 2067.6 ± 2.8 44 ± 6 2368 ± 149 1.382 ± 0.137 465 21 66.2 ± 0.9 38 ± 5 2336± 26 1.411 ± 0.061 524 22 71.0 ± 5.5 38 ± 6 2335 ± 39 1.378 ± 0.085 47423 66.3 ± 1.8 43 ± 5 2211 ± 95 1.395 ± 0.049 480 24 61.8 ± 5.6 37 ± 92093 ± 80 1.321 ± 0.091 527 25 67.0 ± 3.3 46 ± 7 2198 ± 52 1.443 ± 0.065590 26 66.3 ± 6.1 37 ± 13 2290 ± 45 1.554 ± 0.103 628 27 62.0 ± 2.9 42 ±4 2204 ± 58 1.375 ± 0.060 515 28 61.4 ± 2.3 37 ± 8 2146 ± 50 1.352 ±0.026 505 29 57.1 ± 3.2 33 ± 8 1960 ± 130 1.218 ± 0.062 452 30 66.5 ±7.3 46 ± 4 2263 ± 38 1.427 ± 0.068 521 31 72.1 ± 3.7 46 ± 3 2264 ± 1331.334 ± 0.065 424 32 79.1 ± 7.1 43 ± 9 2648 ± 31 1.458 ± 0.053 395 3364.7 ± 1.2 33 ± 5 2567 ± 52 1.413 ± 0.080 474 34 63.8 ± 2.8 39 ± 4 2339± 60 1.431 ± 0.061 524 35 69.0 ± 4.6 52 ± 5 1437 ± 65 0.797 ± 0.104 3661.4 ± 6.6 48 ± 2 2014 ± 118 1.180 ± 0.048 446 37 49.5 ± 0.1 71 ± 3 1861± 69 1.963 ± 0.090 1831

Example 4 Strip Force for Coated Optical Fibers

Optical fibers were coated using one of the primary coating compositionsdetailed below and the curable compositions of the present invention toform the secondary coating. Primary coating composition A included 52 wt% BR3731, available from Bomar Specialties; 45 wt % PHOTOMER 4003,available from Cognis; 1.5 wt % IRGACURE 184 and 1.5 wt % IRGACURE 819,each of which is available from CIBA; 1 pph IRGANOX 1035, which isavailable from Ciba; 2 pph bis(trimethoxysilylethyl)benzene; and 0.3 pph(3-mercaptopropyl)trimethoxysilane. Primary coating composition Bincluded 52 wt % BR3741; 25 wt % PHOTOMER 4003; 20 wt % TONE M-100; 1.5wt % IRGACURE 819; 1.5 wt % IRGACURE 184; and 1 pph(3-acryloxypropyl)trimethoxysilane. Table 6 shows the average peak fiberstrip force at 23° C. for five optical fibers according to the presentinvention.

TABLE 6 Primary Coating Secondary Coating Average Peak Strip CompositionComposition Force (lb force) A 1 0.534 A 2 0.774 A 3 0.710 A 13  0.709 B36  0.618

Example 5 Effect of Young's Modulus on Recoat Strength

Young's modulus values were generated by preparing coated rods whichwere approximately 22–23 mm in diameter after curing. The rods were madeby injecting the recoat formulation into Teflon tubing with an innerdiameter of 25 mm. The rods were then cured using a Fusion UV-systemwith a D bulb at a dosage of about 2400 mk·cm⁻². The Teflon tubing wasstripped following cure, and then the resulting rods were allowed tocondition overnight in a controlled environment of 50% humidity and 23°C. The samples were tested using a Sintech MTS Tensile Tester. Samplegauge length was 5.1 cm and test speed was 2.5 cm/minute. For eachrecoat formulation, ten samples were tested by pulling to failure. Thereported result, in Table 7 below, is the average of the ten samples.

Butt splice samples were prepared in a similar manner described above,using pieces of glass rod inserted into the Teflon tubing. The filledTeflon tubing was cut to prepare ten samples (each containing a buttsplice), and then cured as described above. The Teflon tubing wasremoved from the recoat section, and the interface was examined under amicroscope and marked on either side (with a marker). The butt splicetensile values were generated using the same equipment with the gaugelength decreased to 0.5 cm. Samples were pulled to failure; any samplesthat did not fail at the interface were not included in calculations.

TABLE 7 Rod and Butt Splice Tube Recoat Young's Fracture Tensile TensileFormu- Modulus Toughness, Strength Strength lation (MPa) (K_(c)) (MPa)(MPa) DSM  84.85 ± 8.66 n.a. 22.79 ± 2.71 20 ± 4 950-200 (prior art) DSM 907.28 ± 37.02 1.1955 ± 0.0565 40.77 ± 4.03 58 ± 3 950-105 (prior art)101  800.91 ± 22.14 n.a.  35.4 ± 2.08 48 ± 3  39 1453.56 ± 20 0.6993 ±0.0453 40.36 ± 3.00 53 ± 3  38 2059.77 ± 31.52 1.1756 ± 0.0565 40.58 ±5.18 59 ± 3  40 1964.38 ± 204.26 n.a. 43.37 ± 3.76 n.a.DSM-200 is a commercially available re-coat formulation and DSM-105 is acommercially available secondary coating formulation, both from DSMDesotech. DSM-200 is characterized by a low Young's modulus and is proneto develop gaps at the recoat-fiber interface after events that placestress on the splice junction. DSM-105 is a high fracture toughnesssecondary coating. Formulation 101 is an 80:20 mixture of DSM-200 andDSM-105. Rod and tube tensile strength values were generated by using amethod which was developed to quantify the interfacial strength betweensplice joint recoat materials and the coating on the optical fiber. Acoated optical fiber is cleaved, for example using a commerciallyavailable cleaving tool, through the coating, thereby forming an endfacewhere the coating is flush with the glass end. Two coated fiber endsprepared in this way are placed in a conventional fiber splice recoatmachine with a gap between the fiber ends of approximately 1 to 2centimeters. The gap is filled with the desired splice recoat materialand cured in the usual fashion. The specimen is then removed from therecoat machine and, thereby, as illustrated in FIG. 9, consists of twocoated optical fibers 201 and 202. The fibers have been joined by alength of solid recoat material 205. The recoat material is then cutnear the endface of one of the fibers (e.g. near coating 204) and thefiber 202 pulled therefrom, thereby separating that one fiber (202) fromthe recoat material 205. What remains is a coated fiber 201 with a rodof recoat material 205 on the end. The other optical fiber is thenremoved from its coating jacket 203 to leave a tube of coating, byplacing the coated fiber 201 in liquid nitrogen to temporarily stiffenthe fiber 201 to facilitate removal of the fiber 201 from the coating203, after which point the glass fiber can be pulled off of the coatingusing a stripping tool (e.g. a device used to remove the protectivecoating from electrical wires). In other words, the fiber is pulledthrough a hole just big enough for the fiber to fit through and thecoating is stopped on the other side. By removing the fiber in this way,the resultant test specimen consists of a hollow tube of polymer coatingfrom the original coated fiber with a rod of recoat material attached toit. In this way, the adhesion between the recoat material and the fibercoating can be tested, for example the specimen may be strength testedin tension on a universal testing machine such as an Instron, MTS, etc.

The above-data indicates that higher strength coatings, having a Young'smodulus of 1200 MPa exhibit improved tensile strength and in stress toform gaps. Surprisingly, DSM-105, when used as a re-coat, exhibited highstrength despite a Young's modulus lower than 1200 MPa. Re-coatformulation 38 is characterized by a high Young's modulus, whichnormally would make the formulation too brittle. Surprisingly, that wasnot the case, as this recoat formulation performed exceptionally well inboth tensile strength and stress to form gap between recoat and fibercoating.

Example 6 Effect of Photoinitiator and Degree of Cure on Gap Performance

DSM-950 and formulation 101 were modified by the addition of 1 wt %Irgacure 819 photoinitiator (containing BAPO). Coating gap performancewas then compared to those of the parent formulations. Gap performancewas measured by placing a length of fiber, with a spliced and recoatedsection positioned in the middle, onto a typical tensile testing machine(Instron, MTS, Etc.). The load is increased until a gap forms betweenthe recoat material and the fiber coating. Gap formation is detectedvisually. The load on the glass portion of the fiber when the gap formsis recorded and converted to stress. The results of the testing arepresent in Table 8 below.

TABLE 8 Cure Recoat Degree Stress to Form Std. Recoat Time (s) of Cure(%) Gap (kpsi) Deviation DSM-200 9  90* 201 44 60  102* 217 47 DSM-200 988 188 42 w/Irgacure 819 60  96 183 45 101 9 79  96 18 9 76 112 20 9 87*  77 27 60  101* >XX ND 101 w/Irgacure 9 86 181 33 819 60  95 >220 ND *Degree of Cure measured using old approach which overestimatedvalue; other values measured with new approach are more accurate.There was no significant difference in the observed results using theDSM-200 coating with and without the photoinitiator. Formulation 101showed an improvement in the stress to form gap test at the 9 secondcure rate upon addition of Irgacure 819. With the addition of theIrgacure, the coating was able to sustain nearly twice as great a stressbefore forming gaps at the fiber interface.

Puncture resistance was measured in the following manner. A 4-centimeterlength of fiber is placed on a 3 mm-thick glass slide. One end of thefiber is attached to a device that allows one to rotate the fiber in acontrolled fashion. This fiber is examined under 100× magnificationusing transmitted light and is rotated until the secondary coating wallthickness is equivalent on both sides. In this position the secondarycoating will be thickest at the top or bottom and equal on the sides.This is shown in exaggerated fashion in FIG. 7. This orientation is thenfixed by taping the fiber to the slide at both ends. Indentation iscarried out using an inverted microscope placed beneath the crosshead ofa universal-testing machine. The microscope objective was positioneddirectly beneath a 75° diamond wedge indenter. The glass slidecontaining the fiber is placed on the moveable microscope stage andpositioned directly beneath the indenter such that the width of thewedge is orthogonal to the direction of the fiber. Precise positioningis accomplished by lowering the indenter tip into view along with thefiber and then visually aligning the fiber through movement of the slideon the stage.

Once the fiber is in place the diamond wedge is lowered until it justtouches the coating surface. The wedge is then driven into the coatingat a rate of 0.1 mm/min. The load increases until it suddenly drops,signifying that the coating has been punctured. As viewed from themicroscope, the drop in load corresponds to visual confirmation that thecoating has been punctured. The peak load at puncture is recorded forten such measurements and then the fiber is rotated 180° so that theother extreme of the secondary wall thickness can be tested in the samemanner. Thus, twenty measurements are obtained for a given section offiber.

The results, shown in FIG. 8, illustrate that puncture resistancedepends linearly on the cross-sectional area of the secondary coatingregardless of glass diameter or the presence of primary coating, Theline in FIG. 8 illustrates the linear puncture resistance of a singlelayer of CPC-6, a coating which is commercially available from DSMDesotech, Elgin, Ill. This line may be also be expressed as a punctureresistance y in grams equal to 0.0019x+11.255, where x=the crosssectional area in microns² of the coating. Note that SC 89 and SC95,both of which are coatings in accordance with the invention, ezhibit apuncture resistance which is greater than that of CPC-6 at any point onthat line. In other words, the inventive coatings (e.g. 38 and 40) inthis embodiment exhibit a puncture resistance y in grams greater thanabout 0.0019x+11.255, where x=the cross sectional area in microns² ofthe coating. More preferably, the coatings exhibit a puncture-resistancey which is greater than 3 grams greater than 0.0019x+11.255, where x=thecross sectional area in microns² of the coating.

The white squares in FIG. 8 are the puncture resistance of a commonrecoat material from DSM. Note that this material does not exhibit apuncture resistance higher than the CPC6 data line.

The white triangles in FIG. 8 is a composition very similar to CPC6. Theinventive coatings (e.g. all of the coatings in Table 4) not onlyexhibit a puncture resistance that exceeds that of CPC-6, they alsopreferably exhibit a Young's modulus that is at least about 1200 MPa,more preferably greater than about 1400 MPa, and most preferably greaterthan about 1800 MPa.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A coated optical fiber comprising: first and second optical fibersegments, each comprising an optical fiber having at least one coatingthereon, which at least one coating has been removed from an end sectionthereof, the end sections of the first and second optical fiber segmentsabutting one another end-to-end; and a cured splice-junction coatingthat encapsulates the end sections and contacts the at least one coatingof the first and second optical fiber segments; wherein thesplice-junction coating is characterized by (i) a Young's modulus thatis at least about 1200 MPa, and (ii) an interfacial strength as measuredby the rod and tube method of greater than about 25 MPa.
 2. The coatedoptical fiber according to claim 1 wherein the splice junction coatingis characterized by a Young's modulus that is at least about 1500 MPa.3. The coated optical fiber according to claim 2 wherein the splicejunction coating is characterized by a fracture toughness of at leastabout 0.7 MPa·m^(1/2).
 4. The coated optical fiber according to claim 1wherein the thickness of the splice-junction coating is between about 40microns and about 125 microns.
 5. The coated optical fiber according toclaim 1 wherein splice-junction coating is the cured polymer product ofa composition comprising at least one monomer, at least one oligomer,and at least one polymerization initiator.
 6. A method of re-coating anoptical fiber at a splice junction, said method comprising: providingfirst and second optical fiber segments, each comprising an opticalfiber having at least one coating thereon, which at least one coatinghas been removed from an end section thereof, the end sections of thefirst and second optical fiber segments abutting one another end-to-end;and applying a coating composition to the end sections of the first andsecond optical fibers, whereby the coating composition encapsulates theend sections and contacts the at least one coating of the first andsecond optical fiber segments; and curing the coating composition toform a cured splice-junction coating that is characterized by (i) aYoung's modulus that is at least about 1200 MPa, and (ii) an interfacialstrength as measured by the rod and tube method of greater than about 25MP·a.
 7. The method according to claim 6 wherein coating compositioncomprises at least one monomer, at least one oligomer, and at least onepolymerization initiator.
 8. The method according to claim 7 wherein theat least one polymerization initiator is a photoinitiator.
 9. The methodaccording to claim 8 wherein said curing comprises exposing the coatingcomposition to a UV source.
 10. The method of claim 1, wherein theinterfacial strength as measured by the rod and tube method is greaterthan 35 MPa.
 11. A coated optical fiber comprising: first and secondoptical fiber segments, each comprising an optical fiber having at leastone coating thereon, which at least one coating has been removed from anend section thereof, the end sections of the first and second opticalfiber segments abutting one another end-to-end; and a curedsplice-junction coating that encapsulates the end sections and contactsthe at least one coating of the first and second optical fiber segments;wherein the splice-junction coating is characterized by (i) a Young'smodulus that is at least about 1200 MPa, and (ii) and a punctureresistance y in grams greater than about 0.0019x+11.255, where x=thecross sectional area in microns² of the coating.
 12. The coated opticalfiber according to claim 11 wherein the splice junction coating ischaracterized by a Young's modulus that is at least about 1500 MPa. 13.The coated optical fiber according to claim 12 wherein the splicejunction coating is characterized by a fracture toughness of at leastabout 0.7 MPa·m^(1/2).
 14. The coated optical fiber according to claim11 wherein the thickness of the splice-junction coating is between about40 microns and about 125 microns.
 15. The coated optical fiber accordingto claim 11 wherein splice-junction coating is the cured polymer productof a composition comprising at least one monomer, at least one oligomer,and at least one polymerization initiator.
 16. A method of re-coating anoptical fiber at a splice junction, said method comprising: providingfirst and second optical fiber segments, each comprising an opticalfiber having at least one coating thereon, which at least one coatinghas been removed from an end section thereof, the end sections of thefirst and second optical fiber segments abutting one another end-to-end;and applying a coating composition to the end sections of the first andsecond optical fibers, whereby the coating composition encapsulates theend sections and contacts the at least one coating of the first andsecond optical fiber segments; and curing the coating composition toform a cured splice-junction coating that is characterized by (ii) aYoung's modulus that is at least about 1200 MPa, and (ii) a punctureresistance y in grams greater than about 0.0019x+11.255, where x=thecross sectional area in microns² of the coating.
 17. The methodaccording to claim 16 wherein coating composition comprises at least onemonomer, at least one oligomer, and at least one polymerizationinitiator.
 18. The method according to claim 17 wherein the at least onepolymerization initiator is a photoinitiator.
 19. The method accordingto claim 18 wherein said curing comprises exposing the coatingcomposition to a UV source.